I have been working in glass since 2001. When I retired from the Air Force in 2007, I started working in glass full time. Currently, screen printing and weaving glass are my favorite techniques. I teach a few classes each year at John C. Campbell Folk School. My business name is Di-Fused Glass.
Pros These work well for coloring shelf paper as an inclusion and, when crushed to a powder and mixed with water and a binder, as a watercolor-like paint. You can also just sift the powder onto the glass, then fire.
Cons As crayons, these are pretty worthless. These do not transfer color evenly to either sand-blasted or acid-etched glass.
Other Thoughts I hated these chalks at first. They wouldn't apply evenly on either sand-blasted or acid-etched glass. There were large spaces with no color and clumps of powder. Then I decided to try some other way to use them since I'd invested the money and they were useless as chalks. I took my nugmeg microplane grater and shaved off a small amount of the crayon (using a dust mask). I mixed this with water and various mixing media, then fired to a tack fuse. The result was a beautiful translucent wash of color. I found flat 7-Up worked best as a binder. When uncapped, the surface was matte. You can also cap it with another piece of glass. You get a nice amount of powder from just an 1/8" of chalk, so now I'm happy with my purchase.
1/4" Hollow Mandrel
Works great to blow small pieces in the torch and is much cheaper than task-specific blow pipe with shaped mouthpiece.
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